This invention relates generally to cryogenic air separation and, more particularly, to the preparation of feed air for the cryogenic air separation.
In the cryogenic separation of air using one or more distillation columns to produce one or more products such as nitrogen, oxygen and argon, the feed air is compressed, cleaned of high boiling impurities, and cooled prior to passage into the column or columns of the plant. The operation of the feed air compressor or compressors consumes a significant amount of power, and any improvement which can serve to reduce the compressor power consumption associated with the operation of a cryogenic air separation plant would be very desirable.
Accordingly it is an object of this invention to provide a feed air preparation system which can serve to decrease the compressor power consumption associated with the operation of a cryogenic air separation plant.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for precooling and scrubbing feed air for a cryogenic air separation plant comprising:
(A) passing nitrogen vapor taken from a cryogenic air separation plant to a feed air precooler/scrubber and warming the nitrogen vapor within the feed air precooler/scrubber by heat exchange with water to produce chilled water;
(B) directly contacting the chilled water with feed air containing particulate matter to cool the feed air and to scrub particulate matter from the feed air; and
(C) passing the cooled and scrubbed feed air out from the feed air precooler/scrubber for passage on to the cryogenic air separation plant.
Another aspect of the invention is:
A feed air precooler/scrubber comprising:
(A) an evaporative cooling section, means for providing nitrogen vapor from a cryogenic air separation plant to the evaporative cooling section, and means for passing water to the evaporative cooling section;
(B) a chilling and scrubbing section, means for passing water from the evaporative cooling section to the chilling and scrubbing section, and means for passing feed air into the chilling and scrubbing section; and
(C) means for withdrawing feed air from the chilling and scrubbing section for passage on to the cryogenic air separation plant.
As used herein the terms xe2x80x9cprecoolingxe2x80x9d and xe2x80x9cprecoolerxe2x80x9d mean respectively method and apparatus for cooling feed air prior to the passage of the feed air to the main or primary heat exchanger of a cryogenic air separation plant.
As used herein the term xe2x80x9ccolumnxe2x80x9d means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. 
The term xe2x80x9cdouble columnxe2x80x9d is used to mean a higher pressure column having its upper portion in heat exchange relation with the lower portion of a lower pressure column. A further discussion of double columns appears in Ruheman xe2x80x9cThe Separation of Gasesxe2x80x9d, Oxford University Press, 1949, Chapter VII, Commercial Air Separation.
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Distillation is the separation process whereby heating of a liquid mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases can be adiabatic or nonadiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cnitrogen vaporxe2x80x9d means a gas having a nitrogen concentration of at least 78 mole percent.
As used herein the term xe2x80x9cfeed airxe2x80x9d means a mixture comprising primarily oxygen and nitrogen, such as ambient air.
As used herein the terms xe2x80x9cupper portionxe2x80x9d and xe2x80x9clower portionxe2x80x9d mean those sections of a column respectively above and below the mid point of the column.
As used herein the term xe2x80x9cdirect heat exchangexe2x80x9d means the transfer of heat through contact of cooling and heating entities.